File Migration on the Cray Y-MP at the National Center for Atmospheric Research

Ethan L. Miller

The supercomputer center at the National Center for Atmospheric Research (NCAR) migrates large numbers of files to and from its mass storage system (MSS) because there is insufficient space to store them on the Cray supercomputer's local disks. This paper presents file migration data collected over a 10 month period and some analysis of the data. The analysis shows that requests to the MSS are periodic, with one day and one week periods. Read requests to the MSS account for the majority of the periodicity; write requests are relatively constant over the course of a week. The intervals between requests to the MSS appear to be bunched, since well over half of the intervals are shorter than half the mean interval length. The latencies to access the first byte from disk, automated tape library, and manually-mounted tape are examined. In addition, information about file size distribution is given. We found that the NCAR system was different from systems studied earlier in several ways, including the ratio of local disk to tertiary storage. These differences affect the way that file migration can be done, so previous migration algorithms may not be effective.

BibTeX citation:

@techreport{Miller:CSD-91-638,
Author = {Miller, Ethan L.},
Title = {File Migration on the Cray Y-MP at the National Center for Atmospheric Research},
Institution = {EECS Department, University of California, Berkeley},
Year = {1991},
Month = {Jun},
URL = {http://www.eecs.berkeley.edu/Pubs/TechRpts/1991/5530.html},
Number = {UCB/CSD-91-638},
Abstract = {The supercomputer center at the National Center for Atmospheric Research (NCAR) migrates large numbers of files to and from its mass storage system (MSS) because there is insufficient space to store them on the Cray supercomputer's local disks. This paper presents file migration data collected over a 10 month period and some analysis of the data. The analysis shows that requests to the MSS are periodic, with one day and one week periods. Read requests to the MSS account for the majority of the periodicity; write requests are relatively constant over the course of a week. The intervals between requests to the MSS appear to be bunched, since well over half of the intervals are shorter than half the mean interval length. The latencies to access the first byte from disk, automated tape library, and manually-mounted tape are examined. In addition, information about file size distribution is given. We found that the NCAR system was different from systems studied earlier in several ways, including the ratio of local disk to tertiary storage. These differences affect the way that file migration can be done, so previous migration algorithms may not be effective.}
}